Charge-transporting varnish

ABSTRACT

A charge-transporting varnish is disclosed which comprises a charge-transporting material composed of an oligoaniline compound represented by the formula (1) below and at least one kind of solvent. In this charge-transporting varnish, the charge-transporting material is dissolved or homogeneously dispersed in the solvent. By using this varnish, a charge-transporting thin film having excellent conductive characteristics can be formed through a short-time firing. In particular, when the varnish is applied to an OLED element or a PLED element, the resulting element can achieve excellent element characteristics such as low driving voltage, high luminous efficiency and long life

This application is a 371 filing of PCT/JP04/07118, filed 19 May 2004.

TECHNICAL FIELD

This invention relates to a charge-transporting varnish and, moreparticularly, to a charge-transporting varnish capable of forming, forexample, a charge transporting thin film which is able to improveelectric characteristics and life characteristic while preventingconcentration phenomena of electric current and charge. Thischarge-transporting varnish is applicable as an organicelectroluminescent (hereinafter referred to as EL) element, a capacitorelement, an antistatic film and the like.

BACKGROUND ART

Organic EL elements, particularly, low molecular weight organic EL(hereinafter referred to as OLED), have been isolated function thereofby Eastman Kodak based on ultrathinning and multilayering of organiclayers and are thus remarkably improved in characteristics such asdrastic lowering of drive voltage (Applied Physics Letters, U.S.A.,1987, Vol. 51, pp. 913-915). Cambridge University found an EL elementusing a polymeric fluorescent material (hereinafter referred to as PLED)(Nature, England, 1990, Vol. 347, pp. 539-541), which has now beenimproved in characteristics to such a level as to compare withconventional OLED elements.

On the other hand, it was found that with OLED elements, provision of acopper phthalocyanine (CuPC) layer as a hole injection layer leads to animprovement in initial characteristics such as low drive voltage andhigh luminous efficiency and an effect of prolonging the life of theelements (Applied Physic Letters, U.S.A., 1996, Vol. 69, pp. 2160-2162).With PLED elements, it has been shown that similar effects are obtainedusing, as a hole transporting layer (buffer layer), polyanilinematerials (Nature, England, 1992, Vol. 357, pp. 477-479, Applied PhysicsLetters, U.S.A., 1994, Vol. 64, pp. 1245-1247), and polythiophenematerials (Applied Physics Letters, U.S.A., 1998, Vol. 72, pp.2660-2662). At a cathode side, it has been found that initialcharacteristics could be improved using, as an electron injection layer,metal oxides (IEEE Transactions on Electron Devices, U.S.A., 1997, Vol.44, pp. 1245-1248), metal halides (Applied Physics Letters, U.S.A.,1997, Vol. 70, pp. 152-154), and metal complexes (Japanese Journal ofApplied Physics, 1999, Vol. 38, pp. L1348-1350). These electron layerand buffer layer have been now in general use.

However, CuPC that has been ordinarily used as a hole injection materialin OLED element has the drawback that it has drastic irregularities andthus, brings about a great characteristic lowering upon mixing in otherorganic layers in small amount. Polyaniline-type materials andpolythiophene-type materials currently employed for PLED element involveproblems in that they contain, as a solvent, water having capability ofpromoting element deterioration, limitation is placed on the choice ofsolvent, limitation is also placed on the manner of coating ensuringuniform film formation because of coagulation of material and lowsolubility, and a difficulty is involved in control of viscosity.

Based on the facts set out hereinabove, organic solvent-based chargetransporting varnishes using low molecular weight oligoaniline materialshave been recently found. It has been found that insertion of a holeinjection layer obtained by use of this type of material enablesexcellent EL element characteristics to be shown (see JP-A 2002-151272).

In forming a charge transporting thin film from an oligoanilinecompound, however, long-time firing at high temperature in the presenceof oxygen is usually necessary. Thus, where low molecular weightoligoaniline materials are used as a hole injection layer in OLEDelement or PLED element, a prolonged time is required for thefabrication of the element, so that a problem has been indicated in thelowering of productivity. Hence, there is a demand for shortage of afiring time after the film formation.

DISCLOSURE OF INVENTION

An object of the invention is to provide a charge transporting varnishcapable of achieving excellent conduction characteristics and obtainedthrough firing within a short time in a system using an oligoanilinecompound and a charge accepting dopant material.

As a result of intensive studies for achieving the above object, we havefound that when using a charge transporting varnish obtained bydissolving or homogeneously dispersing, in a solvent, a chargetransporting material being an oligoaniline compound of the followingformula (1), a thin film having conduction characteristics that are asgood as a conventional counterpart can be formed only by firing within ashort time after film formation.

More particularly, the present invention provides the followinginventions [1] to [8].

-   [1] A charge-transporting varnish, characterized by comprising a    charge transporting substance being an oligoaniline compound    represented by the formula (1) and at least one solvent, the charge    transporting substance is dissolved or homogeneously dispersed in    said solvent.

(wherein R¹ represents a hydrogen atom, an unsubstituted or substitutedmonovalent hydrocarbon group, an organooxy group, or an acyl group, R²and R³ independently represent a hydrogen atom, an unsubstituted orsubstituted monovalent hydrocarbon group, or an acyl group, R⁴ to R⁷independently represent a hydrogen atom, a hydroxyl group, anunsubstituted or substituted monovalent hydrocarbon group, an organooxygroup, an acyl group, or a sulfonate group, m and n are independently aninteger of 1 or over and satisfy m+2n≦20, and a quinoid moiety exists atan arbitrary position of the structural formula as tautomerized.)

-   [2] The charge-transporting varnish of [1], characterized in that    the charge transporting substance is a product obtained by oxidizing    an oligoaniline compound represented by the formula (2).

(wherein R¹ represents a hydrogen atom, an unsubstituted or substitutedmonovalent hydrocarbon group, an organooxy group, or an acyl group, R²and R³ independently represent a hydrogen atom, an unsubstituted orsubstituted monovalent hydrocarbon group, or an acyl group, R⁴ to R⁷independently represent a hydrogen atom, a hydroxyl group, anunsubstituted or substituted monovalent hydrocarbon group, an organooxygroup, an acyl group, or a sulfonate group, and m and n areindependently an integer of 1 or over and satisfy m+2n≦20.)

-   [3] The charge-transporting varnish of [1] or [2], characterized by    further comprising a charge accepting dopant substance, the oxidized    product and the charge accepting dopant being dissolved or    homogeneously dispersed in said solvent.-   [4] The charge-transporting varnish of [3], characterized in that    the charge accepting dopant substance is a sulfonic acid derivative    represented by the formula (3).

(wherein D represents a benzene ring, a naphthalene ring, an anthracenering, a phenanthrene ring or a heterocyclic ring, and R⁸ and R⁹independently represent a carboxyl group or a hydroxyl group.)

-   [5] An organic electroluminescent element obtained from the    charge-transporting varnish of any one of [1] to [4].-   [6] An organic electroluminescent element comprising a hole    injection layer formed from the charge-transporting varnish of any    one of [1] to [4].-   [7] An organic electroluminescent element comprising a    hole-transporting layer formed from the charge-transporting varnish    of any one of [1] to [4].-   [8] A charge transporting thin film formed from the    charge-transporting varnish of any one of [1] to [4].

When using a charge transporting varnish of the invention, a chargetransporting thin film can be obtained within a short time withoutlowering productivity according to a simple, inexpensive wet process. Inthis connection, the charge transporting varnish of the inventiondiffers from a conventionally employed charge transporting varnish inthe form of an aqueous solution, and can be used only by use of anorganic solvent.

The formation of a charge transporting thin film of the invention on anelectrode surface can prevent electric short-circuiting. The use of thecharge transporting thin film as a charge injection layer of an organicEL element permits injection barrier to lower owing to the relaxation ofionization potentials of an electrode and an organic layer. In addition,application of conjugated oligomer groups to an organic EL element isenabled. From the foregoing, lowering of luminescence initiating voltageof an organic EL element, improvement of a current efficiency andprolonged life can be achieved.

Further, the charge transporting varnish of the invention is good withrespect to thin film formation process and is useful for application toa capacitor electrode protection film and also to an antistatic film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an infrared absorption spectral chart of phenylpentaanilinesynthesized in Example 1.

FIG. 2 is an infrared absorption spectral chart of oxidizedphenylpentaaniline synthesized in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is described in more detail below.

The charge transporting varnish of the invention is one which contains acharge transporting material serving as a principal component for chargetransporting mechanism and a solvent, or which contains a chargetransporting material, a charge accepting dopant material for improvingcharge transportability and a solvent. In this case, the chargetransporting material (and the charge accepting dopant material) arecompletely dissolved or homogeneously dispersed in the solvent.

The transportability used herein has the same meaning as conductivityand means any one of hole transportability, electron transportability,and transportability of both hole and electron. The charge transportingvarnish of the invention may exhibit charge transportability in itself,or may exhibit charge transportability after conversion to a solid filmobtained by use of the varnish.

The charge transporting material used in the present invention is anoligoaniline compound represented by the formula (1).

(wherein R¹ represents a hydrogen atom, an unsubstituted or substitutedmonovalent hydrocarbon group, an organooxy group, or an acyl group, R²and R³ independently represent a hydrogen atom, an unsubstituted orsubstituted monovalent hydrocarbon group, or an acyl group, R⁴ to R⁷independently represent a hydrogen atom, a hydroxyl group, anunsubstituted or substituted monovalent hydrocarbon group, an organooxygroup, an acyl group, or a sulfonic acid group, m and n areindependently an integer of 1 or over provided that m+2n≦20, and aquinoid moiety tautomerically exists at an arbitrary position of thestructural formula.)

The substituent R¹ of the oligoaniline compound used in the invention ishydrogen, an unsubstituted or substituted monovalent hydrocarbon group,an organooxy group, or an acyl group, and R² and R³ independentlyrepresent a hydrogen atom, an unsubstituted or substituted monovalenthydrocarbon group, or an acyl group.

The monovalent hydrocarbon group and the organooxy group shouldpreferably have 1 to 20 carbon atoms, and the acyl group shouldpreferably have 2 to 20 carbon atoms. The monovalent hydrocarbon groupincludes, for example, an alkyl group such as a methyl group, an ethylgroup, a propyl group, a butyl group, a t-butyl group, a hexyl group, anoctyl group, an decyl group or the like, a cycloalkyl group such as acyclopentyl group, a cyclohexyl group or the like, a bicycloalkyl groupsuch as a bicyclohexyl group or the like, an alkenyl group such as avinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenylgroup, a 1-methyl-2-propenyl group, a 1, 2 or 3-butenyl group, a hexenylgroup or the like, an aryl group such as a phenyl group, a xylyl group,a tolyl group, a biphenyl group, a naphthyl group or the like, anaralkyl group such as a benzyl group, a phenylethyl group, aphenylcyclohexyl group or the like, or a group wherein part or all ofthe hydrogen atoms of these monovalent hydrocarbon groups aresubstituted with a halogen atom, a hydroxyl group, an alkoxy group orthe like.

As an organooxy group includes an alkoxy group, an alkenyloxy group, anaryloxy group or the like. For these alkyl group, alkenyl group and arylgroup, mention is made of such groups as exemplified above.

The acyl group includes one having 2 to 10 carbon atoms such as, forexample, an acetyl group, a propionyl group, a butyryl group, anisobutyryl group, a valeryl group, an isovaleryl group, a benzyl groupor the like.

Preferred examples of R¹ and R² include a hydrogen atom, an alkyl grouphaving 1 to 20 carbon atoms, preferably 1 to 4 carbon atoms, a phenylgroup, a cyclohexyl group, a cyclopentyl group, a biphenyl group, abicyclohexyl group or a phenylcyclohexyl group (provided these phenyl,cyclohexyl, cyclopentyl, biphenyl, bicyclohexyl and phenylcyclohexylgroups may have a substituent such as an alkyl group or an alkoxy grouphaving 1 to 4 carbon atoms.), or an acyl group having 2 to 4 carbonatoms. For R³, a hydrogen atom, an alkyl group having 1 to 4 carbonatoms, or a phenyl group which may have an alkoxy group as a substituentis preferred.

Especially, the case where R¹ is a hydrogen atom and R³ is a phenylgroup, i.e., the oligoaniline compound of the formula (1) is blockedwith a phenyl group at both ends thereof, is preferred.

The substituents R⁴ to R⁷ independently represent a hydrogen atom, ahydroxyl group, an unsubstituted or substituted monovalent hydrocarbongroup, an organooxy group, an acyl group, and a sulfonic acid group. Theunsubstituted or substituted monovalent hydrocarbon group and organooxygroup should preferably have 2 to 20 carbon atoms, respectively, and theacyl group should preferably have 2 to 20 carbon atoms, and mention maybe made of those groups as indicated with respect to R¹.

The substituents R⁴ to R⁷ preferably include a hydrogen atom, an alkylgroup, an alkoxy group, an alkoxyalkyl group, an alkenyl group, an acylgroup, a sulfonic acid group, and a hydroxyl group, or a phenyl group, acyclohexyl group, a cyclopentyl group, a biphenyl group, a bicyclohexylgroup or a phenylcyclohexyl group that may have a substituent of analkyl group or alkoxy group each having 1 to 4 carbon atoms.

More preferably, R⁴ to R⁷ represents a hydrogen atom, an alkyl grouphaving 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbonatoms, an alkoxyalkyl group wherein the alkoxy group has 1 to 20 carbonatoms and the alkyl group has 1 to 20 carbon atoms, an alkenyl grouphaving 2 to 4 carbon atoms, an acyl group having 2 to 4 carbon atoms, abenzoyl group, a sulfonic acid group, a hydroxyl group, or a phenylgroup, a cyclohexyl group, a cyclopentyl group, a biphenyl group, abicyclohexyl group or a phenylcyclohexyl group that may have asubstituent (wherein the substituent includes an alkyl group having 1 to4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms),respectively. Most preferably, mention is made of a hydrogen atom, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, an alkoxyalkyl group wherein the alkoxy group has 1 to 4carbon atoms and the alkyl group has 1 to 4 carbon atom, a vinyl group,a 2-propenyl group, an acetyl group, a benzoyl group, a sulfonic acidgroup, a hydroxyl group, or a phenyl group, a cyclohexyl group, abiphenyl group, a bicyclohexyl group or a phenylcyclohexyl group thatmay have a substituent (wherein the substituent includes an alkyl grouphaving 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbonatoms), respectively. It will be noted that in the two benzene rings ofthe formula (1), the substituents indicated by the same symbol may bethe same or different.

The numbers of m and n at the oligoaniline moiety are independently aninteger of 1 or over. It is preferred that a ratio of m to n is 2 orover. Where solubility in a solvent for charge transporting material istaken into account, m+2n should preferably be 20 or below. Where asolution having a high concentration of 20 wt % or over is prepared, avalue of 10 or below, preferably 5 or below is preferred.

The charge transporting material of the formula (1) can be obtained byoxidizing an oligoaniline compound of the formula (2).

(wherein R¹ to R⁷ , m and n are, respectively, the same as definedhereinbefore.)

When taking enhanced solubility and uniform charge transportability intoaccount, the oligoaniline compound represented by the formula (2) shouldpreferably one which has no distribution of molecular weight, i.e., adegree of dispersion is at 1.

Specific examples of such an oligoaniline compound are thoseoligoaniline compounds soluble in organic solvents, such asphenyltetraaniline, phenylpentaaniline and the like. With respect to thesynthesis of this type of oligoaniline compound, mention is made ofsynthetic processes set forth, for example, in Bulletin of ChemicalSociety of Japan, 1994, Vol. 67, pp. 1749-1752) and Synthetic Metals,U.S.A., 1997, Vol. 84, pp. 119-120) although not limited to these ones.

The oxidation treatment carried out for the oligoaniline compound of theformula (2) is performed by a procedure wherein after dissolving theoligoaniline compound in an appropriate solvent, for example, chemicaloxidation is carried out by use of an appropriate oxidizing agent, orwherein while heating a powder or solution of the oligoaniline compound,oxidation is carried out in air or in the presence of oxygen understirring, although not limited to these procedures.

For the solvent used for carrying out the oxidation treatment, althoughmention is made specifically of N,N-dimethylformamide,N,N-dimethylacetamide, N-methylpyrrolidone,N,N′-dimethylimidazolidinone, dimethylsulfoxide, chloroform,tetrahydrofuran, 1,4-dioxane, toluene, xylene and the like, nolimitation is placed so far as those capable of dissolving theoligoaniline are used. These may be used singly or in admixture.

Specific examples of an oxidizing agent used for carrying out theoxidation treatment include a halogen such as chlorine, bromine, iodineor the like, an inorganic acid such as nitric acid, sulfuric acid or thelike, an inorganic oxidizing agent such as ozone, hydrogen peroxide,potassium permanganate, potassium dichromate, sulfur dioxide and thelike, and organic oxidizing agent such as 7,7,8,8-tetacyaoquinodimethane(TCNQ) and derivatives thereof, 1,1,2,2-tetracyanoethylene (TCNE),2,3-dichloro-5,6-dicyano-1,4-enzoquinone (DDQ), chloranil and bromanilalthough not limited to these compounds.

As the charge accepting dopant material used in the invention, anelectron accepting dopant material is used for a hole transportingmaterial and a hole accepting dopant material is used for an electrontransporting material, and both should favorably have high chargereceptivity. As to solubility, no limitation is placed so far as thosematerials capable of being dissolved in at least one solvent are used.

Specific examples of the electron accepting dopant include inorganicstrong acids such as hydrogen chloride, sulfuric acid, nitric acid andphosphoric acid, Lewis acids such as aluminium (III) chloride (AlCl₃),titanium (IV) tetrachioride (TiCl₄), boron tribromide (BBr₃),borontrifluoride complex (BF₃OEt₂), iron (III) chloride (FeCl₃), copper(II) chloride (CuCl₂), antimony pentachioride (SbCl₅), arsenic (V)pentafluoride (AsF₅), phosphorus pentafluoride (PF₅),tri(4-bromophenyl)aluminium hexachloroantmonate ((TBPAH) and the like,organic strong acids such as benzenesulfonic acid, tosyl acid,camphorsulfonic acid, hydroxybenzensulfonic acid, 5-sulfosalicylic acid,dodecylbenzenesulfonic acid, polystyrenesulfonic acid and the like, andorganic or inorganic oxidizing agents such as TCNQ and derivativesthereof, DDQ and iodine although not limited to these compounds.

Specific examples of the hole accepting dopants include alkali metals(Li, Na, K, Cs) and metal complexes such as lithium quinolinoate (Liq)and lithium acetylacetonate (Li(acac)), and the like although notlimited to these dopants. Both of the charge transporting material andcharge accepting dopant material should preferably be in the form of anamorphous solid. If either or both are not in the form of an amorphoussolid, it has found as a result of combination of both the chargetransporting material and charge accepting dopant substance and asolvent indicated hereinafter that materials capable of exhibiting anamorphous solid property after film formation are preferred. Whereeither or both of the charge transporting material and charge acceptingdopant material are in the form of a crystalline solid, at least one ofthe materials should preferably have random intermolecular interaction.With a low molecular weight compound, those materials having, forexample, three or more different polar functional groups in the samemolecule are favorable. Although not limitative, such compounds include,for example, Tiron, dihydroxybenzenesulfonic acid and sulfonic acidderivatives represented by the formula (3) and the like. Of these, thesulfonic acid derivatives represented by the formula (3) are preferred.Specific examples of the sulfonic acid derivative includesulfosalicyclic acid derivatives, e.g., 5-sulfosalicyclic acid and thelike.

(wherein D represents a benzene ring, a naphthalene ring, an anthracenering, a phenanthrene ring or a heterocyclic ring, and R⁸ and R⁹independently represent a carboxyl group or a hydroxyl group.)

The solvent used for obtaining the charge transporting varnish of theinvention is not critical provided that it is able to dissolve a chargetransporting material having been subjected to oxidation treatment, andit is preferred that the varnish is in a state where completelydissolved or homogeneously dispersed. Specific examples of the solventsinclude water, methanol, N,N-dimethylformamide, N,N-dimethylacetamide,N-methylpyrrolidone, N,N′-dimethylimidazolidinone, dimethylsulfoxide,chloroform, toluene, methanol and the like solvent. These may be usedsingly or in admixture.

A highly viscous solvent may be mixed for the purpose of obtaining avarnish having high viscosity within a range of not impeding solubility.Specific examples include cyclohexanol, ethylene glycol, ethylene glycoldiglycidyl ether, 1,3-octylene glycol, diethylene glycol, dipropyleneglycol, triethylene glycol, tripropylene glycol, 1,3-butandiol,1,4-butandiol, propylene glycol, hexylene glycol and the like althoughnot limited to these solvents.

Further, solvents for imparting flatness to a film upon firing for thepurposes of improving wettability against a substrate, control insurface tension of a solvent, control of polarity, control of a boilingpoint and the like may be used for the varnish within a range of notimpeding solubility. Specific examples include butyl cellosolve,diethylene glycol diethyl ether, dipropylene glycol monomethyl ether,ethyl carbitol, diacetone alcohol, γ-butyrolactone, ethyl lactate andthe like although not limited to these.

A concentration of a charge transporting material in a solution can becontrolled within the range of 1 to 80 wt %, particularly 1 to 20 wt %.

A charge transporting film can be formed on a substrate by coating thecharge transporting varnish onto the substrate and evaporating thesolvent. Although the manner of coating is not limitative, there arementioned, for example, a dipping method, a spin coating method, atransferring printing method, a roll coating method, an ink jet method,a spraying method, a brushing method and the like. Although the mannerof evaporation of solvent is not critical, it is possible to carry outevaporation by use of a hot plate or an oven in an appropriateatmosphere, i.e., in air or an inert gas such as nitrogen or the like,or in vacuum. The firing temperature is not critical so far as a solventcan be evaporated and is preferably within 40 to 250° C. To ensure moreuniform film formation or to cause the reaction on the substrate toproceed, a temperature may be changed in two or more stages.

With respect to the charge transporting thin film obtained by thecoating and evaporation procedures, the film thickness is not critical,and preferably ranges 5 to 200 nm where used as a charge injection layerof an organic EL element. For a method of changing the film thickness,mention is made of a method wherein a solid content in a varnish ischanged, a method of changing an amount of solution on application to asubstrate, and the like.

The procedure of making an OLED element using the charge transportingvarnish of the invention and the types of materials used may be thosedescribed hereinbelow although not limited thereto.

It is preferred that the electrode substrate used has been cleanedbeforehand through washing with a liquid such as a detergent, analcohol, pure water or the like, and with an anode substrate, a surfacetreatment such as an ozone treatment, an oxygen-plasma treatment or thelike is carried out immediately before use. It is to be noted that wherean anodic material is made principally of an organic matter, the surfacetreatment may not be performed.

Where a hole transporting varnish is used for an OLED element, thefollowing procedure is used.

The hole transporting varnish is applied onto an anode substrateaccording to such a method as set out above to form a hole transportingthin film on the electrode. The substrate is placed into a vacuumevaporation apparatus, followed by successive vacuum deposition of ahole transporting layer, a luminescent layer, an electron transportinglayer, an electron injection layer and a cathodic metal to provide anOLED element. For controlling a luminescent region, a carrier blocklayer may be provided between arbitrary layers.

Mention is made, as an anodic material, transparent electrodes typicalof which are indium tin oxide (ITO) and indium zinc oxide (IZO), and itis preferred to use those subjected to planarization. Alternatively,polythiophene derivatives and polyanilines having high chargetransportability may also be used. For materials forming a holetransporting layer, there are mentioned triarylamines such as(triphenylamine) dimer derivative (TPD), (α-naphthyldiphenylamine) dimer(α-NPD), [(triphenylamine)dimer] spirodimer (spiro-TAD) and the like,starburst amines such as4,4′,4″-tris[3-methylphenyl(phenyl)-amino]triphenylamine (m-MTDATA),4,4′,4″-tris[1-naphthyl-(phenyl)amino]triphenylamine (1-TNATA) and thelike, and oligothiophenes such as5,5″-bis-{4-[bis(4-methylphenyl)-amino]phenyl}-2,2′:5′,2″terthiophene(BMA-3T) and the like.

For the material forming a luminescent layer, mention is made oftris(8-quinolinolate) aluminium (III) (Alq₃), bis(8-quinolinolate) zinc(II) (Znq₂), bis(2-methyl-8-quinolinolate) (p-phenylphenolate) aluminium(III) (BAlq), 4,4′-bis(2,2-diphenylvinyl)biphenyl (DPVBi) and the like.The luminescent layer may be formed by co-deposition of an electrontransporting material or a hole transporting material and a luminescentdopant.

For an electron transporting material, mention is made of Alq₃, BAlq,DPVBi, (2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole) (PBD),triazole derivatives (TAZ), baxoproin (BCP), syrol derivatives and thelike.

For a luminescent dopant, mention is made of quinacridone, rubrene,coumarin 540,4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM),tris(2-phenylpyridine) iridium (III) (Ir(ppy)₃),(1,10-phenanthoroline)-tris(4,4,4-trifluoro-1-(2-thienyl)-butan-1,3-dionate)europium(III) (Eu(TTA)₃phen) and the like.

For a material forming a carrier block layer, PBD, TAZ and BCP arementioned.

For an electron injection layer, mention is made of lithium oxide(Li₂O), magnesium oxide (MgO), alumina (Al₂O₃), lithium fluoride (LiF),magnesium fluoride (MgF₂), strontium fluoride (SrF₂), Liq, Li(acac),lithium acetate, lithium benzoate and the like.

Aluminium, magnesium-silver alloys, aluminium-lithium alloys, lithium,sodium, potassium, cesium and the like are mentioned as a cathodicmaterial.

With the case where the charge transporting varnish of the invention isused as an OLED element, the following procedure is employed.

The electron transporting varnish is used to form an electrontransporting thin film on an anode substrate and is placed into a vacuumdeposition apparatus, and an electron transporting layer, a luminescentlayer, a hole transporting layer and a hole injection layer are formed,followed by film formation of an anodic material a method such assputtering to provide an OLED element.

Although the manner of making a PLED element using the chargetransporting varnish of the invention is not critical, mention is madeof the following procedure.

In the fabrication of the above OLED element, the vacuum depositionoperations of the hole transporting layer, luminescent layer, electrontransporting layer and electron injection layer are not carried out, buta luminescent charge transporting polymer layer is formed thereby makinga PLED element including the charge transporting thin film formed of thecharge transporting varnish of the present invention. More particularly,the hole transporting varnish is applied onto an anode substrate to forma charge transporting thin film on the electrode according to such aprocedure as set out above, on which a luminescent charge transportingpolymer layer is formed, followed by vacuum deposition of a cathodeelectrode to provide a PLED element. Alternatively, the electrontransporting varnish is applied onto a cathode substrate to form anelectron transporting thin film on the electrode according to such aprocedure as set out above, followed by forming a luminescent chargetransporting polymer layer thereon and forming an anode electrode by aprocedure such as sputtering, vacuum deposition, spin coating or thelike, thereby providing a PLED element.

The cathode and anode materials used are those substances as used forfabrication of the above OLED element. A washing treatment and a surfacetreatment in the fabrication of the OLED element can be applied to thefabrication of the PLED element.

For the formation of the luminescent charge transporting polymer layer,there is mentioned a method wherein a solvent is added to a luminescentcharge transporting polymer material or its mixture with a luminescentdopant for dissolution or homogeneous dispersion, followed by coatingonto an electrode substrate on which the hole injection layer has beenformed, and evaporating the solvent to form a film.

For the luminescent charge transporting polymer materials, mention ismade of polyfluorene derivatives such as poly(9,9-dialkylfluorene)(PDAF)and the like, polyphenylenevinylene derivatives such aspoly(2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV) andthe like, polythiophene derivatives such as poly(3-alkylthiophene) (PAT)and the like, and polyvinylcarbazole (PVCz) and the like.

The solvents include toluene, xylene, chloroform and the like, and fordissolution or homogeneous dispersion, there are mentioned dissolutionor homogeneous dispersion methods including stirring, stirring underheat, ultrasonic dispersion and the like.

The manner of coating is not critical and includes, for example, adipping method, a spin coating method, a transferring printing method, aroll coating method, an ink jet method, a spraying method, a brushingmethod and the like. These coating methods is favorably carried out inan inert gas such as nitrogen, argon or the like.

For the evaporation of solvent, there is mentioned a method of heatingin an inert gas or in vacuum with an oven or on a hot plate.

EXAMPLES

The invention is more particularly described by Examples and ComparativeExamples, and the invention should not be construed as limited to thefollowing Examples. It will be noted that “parts” in the followingillustration means “parts by weight”.

Example 1

Referring to the method described in Bulletin of Chemical Society ofJapan, 1994, Vol. 67, pp. 1749-1752, phenylpentaaniline (PPA)represented by the formula (4) was obtained through the reaction betweenp-diaminodiphenylamine and p-hydroxydiphenylamine.

The synthesis of PPA was carried out according to the followingprocedure. That is, 1.00 g of p-diaminodiphenylamine was dissolved in 21ml of toluene, to which 10.21 g of tetra-n-butoxy titanium serving as adehydration condensing agent was added and dissolved. While theresulting reaction solution was maintained at 110° C. under a nitrogenatmosphere, 2.22 g of p-hydroxydiphenylamine dissolved in 42 ml oftoluene was added to, followed by reaction at 110° C. under a nitrogenatmosphere for 48 hours. After completion of the reaction, the reactionsolution cooled down to room temperature was filtered and the resultingfiltrate was washed with toluene and then with diethyl ether and driedto obtain a light purple powder.

The thus obtained powder was dissolved by adding 40 parts of dioxane and0.2 equivalents of hydrazine hydrate thereto, purging the reactionsystem with nitrogen and heating under reflux. 16 parts of toluene wasadded to the resulting solution to suspend the solution, followed byheating under reflux and filtering the resulting solution in a hotcondition. The solid precipitated from the filtrate was recrystallized,washed successively with toluene-dioxane (1:2.5) and ether under anitrogen atmosphere, followed by collection through filtration anddrying the resulting crystals under reduced pressure at 60° C. for 10hours. Similar recrystallization operations were repeated once more toobtain 2.07 g (with a yield of 64%) of bluish purple crystals. Theinfrared absorption spectrum of the thus obtained PPA is shown inFIG. 1. The absorption attributed to the N—H stretch vibration wasobserved in the vicinity of 3400 cm⁻¹. In the mass spectrum (MALDI-TOF)of the PPA, a mass peak of m/z=533.18 corresponding to the molecularweight of PPA was observed.

The synthesized PPA was oxidized in the following way. That is, 1.00 gof PPA was dissolved in a mixed solvent of 300 ml of toluene and 50 mlof dioxane, followed by stirring at 110° C. in air for 48 hours tooxidize PPA. The resulting black liquid was filtered, and the solventwas distilled off from the filtrate to obtain 0.93 g (yield: 93%) ofblack powder.

The infrared absorption spectrum of the resulting oxidized PPA is shownin FIG. 2. The N—H stretch vibration at 3400 cm⁻¹ observed in FIG. 1 isreduced in intensity in FIG. 2. In the mass spectrum (MALD1-TOF) of theoxidized PPA, mass peaks of m/z=529.57 and m/z=531.59, which was smallerthan the molecular weight of PPA, were observed. In view of this, it isconsidered that PPA is reliably oxidized by the above oxidationtreatment.

0.43 g of 5-sulfosalicyclic acid and 2.8 g of N,N-dimethylacetamide(DMAc) were added to 0.18 g of the thus obtained, oxidized PPA under anitrogen atmosphere and dissolved. 7.9 g of cyclohexanol was added tothe resulting solution and stirred to provide a varnish (solid content:4.2%). The thin film formation of the resulting varnish on an ITO glasssubstrate was carried out in the following way. An ozone treatment iscarried out for 40 minutes on the ITO glass substrate immediately beforea spin coating on the varnish. More particularly, the varnish was coatedon the substrate according to a spin coating method and fired in air at160° C. and 180° C. to form a 30 nm thick thin film. The firingtemperature and firing time in the course of film formation, andelectric conductivity at room temperature are shown in Table 1.

TABLE 1 Electric conductivity Firing Firing [S/cm] temperature time(under current application Run No. (° C.) (minutes) of 100 mA/cm²) 1 1801 3.82 × 10⁻⁷ 2 180 3 5.20 × 10⁻⁷ 3 180 5 6.19 × 10⁻⁷ 4 180 10 6.16 ×10⁻⁷ 5 180 20 6.29 × 10⁻⁷ 6 180 30 6.62 × 10⁻⁷ 7 180 60 6.72 × 10⁻⁷ 8180 120 7.03 × 10⁻⁷ 9 160 60 1.67 × 10⁻⁷

Example 2

After formation of a hole transporting thin film on an ITO glasssubstrate according to the method set out in Example 1, the substratewas placed into a vacuum deposition apparatus, followed by vacuumdeposition of α-NPD, Alq₃, LiF and Al successively. The film thicknesseswere, respectively, set at 40 nm, 60 nm, 0.5 nm and 100 nm, and thevacuum deposition operations were, respectively, carried out after apressure was at 8×10⁻⁴ Pa or below. The deposition rate was 0.3 to 0.4nm/s except for LiF, and was 0.02 to 0.04 nm/s for LiF. The movementoperations between the vacuum deposition operation cycles were performedin vacuum. The characteristics of the resulting OLED element are shownin Table 2.

TABLE 2 At the time of luminescence of Luminescence 500 cd/m² FiringFiring initiating Current Run temperature time voltage Voltageefficiency No. (° C.) (minutes) [V] [V] [CD/A] 1 180 1 3.5 10.8 2.5 3180 5 3.5 10.6 3.0 4 180 10 3.3 8.3 3.4 6 180 30 3.0 8.1 3.4 7 180 603.0 8.1 3.5 8 180 120 2.8 7.1 4.0 9 160 60 3.0 8.2 3.3

Comparative Example 1

5-Sulfosalicyclic acid (5-SSA), and N,N-dimethylacetamide (DMAc) andcyclohexanol were added to the PPA obtained after synthesis andpurification carried by use of the method described in Example 1 toprepare a varnish.

An ITO glass substrate was subjected to ozone cleaning for 40 minutesimmediately before spin coating of the varnish. The varnish was coatedonto the ITO glass substrate according to the method set out in Example1, followed by firing in air at 160° C. and 180° C. to provide a 30 nmthick thin film. The firing temperature and firing time in the course offilm formation, and electric conductivity at room temperature are shownin Table 3. It will be seen that Example 1 ensures the formation of athin film of higher electric conductivity by firing within a shortertime or at a lower temperature than Comparative Example 1.

TABLE 3 Electric conductivity Firing [S/cm] temperature Firing time(under current application Run No. (° C.) (minutes) of 100 mA/cm²) 10180 1 4.66 × 10⁻⁸ 11 180 3 7.79 × 10⁻⁸ 12 180 5 8.79 × 10⁻⁸ 13 180 101.02 × 10⁻⁷ 14 180 20 2.93 × 10⁻⁷ 15 180 30 3.99 × 10⁻⁷ 16 180 60 5.36 ×10⁻⁷ 17 180 120 6.98 × 10⁻⁷ 18 160 60 5.93 × 10⁻⁸

Comparative Example 2

After formation on an ITO glass substrate as a hole transporting thinfilm by the method set out in Comparative Example 1, the substrate wasplaced into a vacuum deposition apparatus, followed by successive vacuumdeposition of α-NPD, Alq₃,LiF and Al under the same conditions as in themethod set out in Example 1. The characteristics of the resulting OLEDelement are shown in Table 4. Example 2 ensures the fabrication of anorganic EL element with a higher luminescence initiating voltage andhigher efficiency by firing within a shorter time or at a lowertemperature than Comparative Example 2.

TABLE 4 At the time of luminescence of Luminescence 500 cd/m² FiringFiring initiating Current Run temperature time voltage Voltageefficiency No. (° C.) (minutes) [V] [V] [CD/A] 10 180 1 5.0 14.3 2.1 12180 5 4.5 13.2 2.3 13 180 10 4.5 10.6 2.4 15 180 30 3.5 8.6 3.1 16 18060 3.0 8.4 3.5 17 180 120 3.0 8.4 4.0 18 160 60 4.0 8.7 3.1

1. A charge-transporting varnish, comprising a charge transportingsubstance being an oligoaniline compound represented by the formula (1)and at least one solvent, the charge transporting substance is dissolvedor homogeneously dispersed in said solvent;

wherein R¹ represents a hydrogen atom, an unsubstituted or substitutedmonovalent hydrocarbon group, an organooxy group, or an acyl group, R²and R³ independently represent a hydrogen atom, an unsubstituted orsubstituted monovalent hydrocarbon group, or an acyl group, R⁴ to R⁷independently represent a hydrogen atom, a hydroxyl group, anunsubstituted or substituted monovalent hydrocarbon group, an organooxygroup, an acyl group, or a sulfonate group, m and n are independently aninteger of 1 or over and satisfy m+2n≦20, and a quinoid moiety exists atan arbitrary position of the structural formula as tautomerized.
 2. Thecharge-transporting varnish as set forth in claim 1, wherein the chargetransporting substance is a product obtained by oxidizing anoligoaniline compound represented by the formula (2):

wherein R¹ represents a hydrogen atom, an unsubstituted or substitutedmonovalent hydrocarbon group, an organooxy group, or an acyl group, R²and R³ independently represent a hydrogen atom, an unsubstituted orsubstituted monovalent hydrocarbon group, or an acyl group, R⁴ to R⁷independently represent a hydrogen atom, a hydroxyl group, anunsubstituted or substituted monovalent hydrocarbon group, an organooxygroup, an acyl group, or a sulfonate group, and m and n areindependently an integer of 1 or over and satisfy m+2n≦20.
 3. Thecharge-transporting varnish as set forth in claim 1 or 2, furthercomprising a charge accepting dopant substance, the oxidized product andthe charge accepting dopant being dissolved or homogeneously dispersedin said solvent.
 4. The charge-transporting varnish as set forth inclaim 3, wherein the charge accepting dopant substance is a sulfonicacid derivative represented by the formula (3):

wherein D represents a benzene ring, a naphthalene ring, an anthracenering, a phenanthrene ring or a heterocyclic ring, and R⁸ and R⁹independently represent a carboxyl group or a hydroxly group.
 5. Anorganic electroluminescent element obtained from the charge-transportingvarnish as set forth in claim
 1. 6. The organic electroluminescentelement comprising a hole injection layer formed from thecharge-transporting varnish as set forth in claim
 1. 7. The organicelectroluminescent element comprising a hole-transporting layer formedfrom the charge-transporting varnish as set forth in claim
 1. 8. Acharge transporting thin film formed from the charge-transportingvarnish as set forth in claim 1.